(of a bad thing) uncontrolled and widespread; (of plants) growing thick and wild.
Rampant corruption is widespread corruption and is difficult to control. A rampant disease is a disease that has spread over a large area and is uncontrolled. If crime in an area is rampant there is a lot of it and it cannot be checked easily. The rampant growth of plants is widespread and uncontrolled growth of plants. Rampant vegetation is the wild growth of all kinds of trees in a fast manner.

Corruption is so rampant in the country that people there wonder if the country can ever be free from it. The corruption has spread to all sections of the society and successive governments have failed to root it out.

The disease is rampant in the area and it is mainly due to the unhygienic habits of the people. Unless they are made aware of the importance of hygiene the disease cannot be controlled.